Rubber Composition and Pneumatic Tire Manufactured Using Same

ABSTRACT

A rubber composition contains a diene rubber containing a styrene-butadiene copolymer component formed from at least one type of styrene-butadiene copolymers, and a reinforcing filler. The styrene-butadiene copolymer(s) satisfy: (1) a bonded styrene content is from 5 to 50 wt. %; (2) a total of styrene content of an ozone-decomposed component S1 having one styrene-derived unit and styrene content of an ozone-decomposed component S1V1 having one styrene-derived unit and one 1,2-bonded butadiene-derived unit is less than 80 wt. % of the bonded styrene content and a total of styrene content of the ozone-decomposed component S1V1 is less than 10 wt. % of the bonded styrene content; (3) an integrated intensity of an ozone-decomposed component S1V2 having one styrene-derived unit and two 1,2-bonded butadiene-derived units is 15% or greater of an integrated intensity of all ozone-decomposed products containing a styrene-derived unit; and (4) a vinyl content of butadiene moiety is 50% or greater.

TECHNICAL FIELD

The present technology relates to a rubber composition with which rubberstrength and wear resistance are enhanced to or beyond conventionallevels, and a pneumatic tire manufactured using the same.

BACKGROUND ART

In recent years, high wet grip performance and low rolling resistancehave been demanded for pneumatic tires. To satisfy these, technologiesin which a styrene-butadiene copolymer and a reinforcing filler such assilica are blended in a rubber composition constituting a cap tread of atire have been known. Furthermore, to enhance wear resistance and rubberhardness of a rubber composition, for example, blending of polybutadieneand/or highly reactive silica has been proposed; however, in this case,problems of reduction in rubber strength, deterioration ofprocessability, and the like exists.

Japanese Unexamined Patent Application Publication No. 03-239737Adescribes that a pneumatic tire manufactured using a rubber compositioncontaining a styrene-butadiene copolymer having a particular arrangementof styrene-derived units, and silica in a tread can satisfy wet skidresistance, rolling resistance, and wear resistance at the same time.However, this rubber composition cannot always satisfy the demands fromconsumers since the rubber strength thereof decreases.

Japanese Unexamined Patent Application Publication No. 57-179212Adescribes a styrene-butadiene copolymer in which, relative to a totalstyrene content in a styrene-butadiene copolymer, a long chain styreneblock is 5 wt. % or less and one single chain is 50 wt. % or greater instyrene-derived units, and a total content of styrene is 10 to 30 wt. %of the styrene-butadiene copolymer. However, this is not sufficient toenhance rubber strength, wear resistance, and low hysteresis loss ofrubber compositions.

SUMMARY

The present technology provides a rubber composition with which rubberstrength and wear resistance are enhanced to or beyond conventionallevels.

A rubber composition of the present technology includes: a diene rubbercontaining at least one type of styrene-butadiene copolymer and areinforcing filler; a styrene-butadiene copolymer component formed fromthe at least one type of styrene-butadiene copolymer havingcharacteristics (1) to (4) below:

(1) a bonded styrene content being from 5 to 50 wt. %;

(2) when a decomposed component S1 having one styrene-derived unit and adecomposed component S1V1 having one styrene-derived unit and one1,2-bonded butadiene-derived unit are measured by subjecting adecomposed component obtained by ozone decomposition to gel permeationchromatography (GPC), a total of styrene contents of the decomposedcomponent S1 and the decomposed component S1V1 being less than 80 wt. %of the bonded styrene content, and a total of styrene content of thedecomposed component S1V1 being less than 10 wt. % of the bonded styrenecontent;

(3) when the decomposed component obtained by ozone decomposition ismeasured by liquid chromatography-mass spectrometer (LCMS), anintegrated intensity of a decomposed component S1V2 having onestyrene-derived unit and two 1,2-bonded butadiene-derived units being15% or greater of an integrated intensity of all the decomposedcomponents containing a styrene-derived unit; and

(4) a vinyl content of butadiene moiety being 50% or greater.

Since the rubber composition of the present technology contains a dienerubber containing a styrene-butadiene copolymer component and areinforcing filler; the styrene-butadiene copolymer component satisfyingthat, as described above: (1) a bonded styrene content being from 5 to50 wt. %; (2) a total of styrene content of an ozone-decomposedcomponent S1 having one styrene-derived unit and styrene content of anozone-decomposed component S1V1 having one styrene-derived unit and one1,2-bonded butadiene-derived unit being less than 80 wt. % of the bondedstyrene content and a total of styrene content of the ozone-decomposedcomponent S1V1 being less than 10 wt. % of the bonded styrene content;(3) an integrated intensity of an ozone-decomposed component S1V2 havingone styrene-derived unit and two 1,2-bonded butadiene-derived unitsbeing 15% or greater of an integrated intensity of all ozone-decomposedproducts containing a styrene-derived unit; and (4) a vinyl content ofbutadiene moiety being 50% or greater, rubber strength and wearresistance are enhanced to or beyond conventional levels.

The diene rubber preferably further contains at least one type selectedfrom the group consisting of natural rubber, polyisoprene, andpolybutadiene. Furthermore, the reinforcing filler is preferably atleast one type selected from the group consisting of a silica and acarbon black.

The rubber composition described above is preferably used in a pneumatictire and, particularly preferably used in a cap tread. The pneumatictire can enhance rubber strength and wear resistance to or beyondconventional levels.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partial cross-sectional view in a tire meridian directionthat illustrates an example of an embodiment of a pneumatic tire inwhich a rubber composition of the present technology is used.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view that illustrates an example of anembodiment of a pneumatic tire in which a rubber composition is used.The pneumatic tire is formed from a tread portion 1, a sidewall portion2, and a bead portion 3.

In FIG. 1, two layers of a carcass layer 4, formed by arrangingreinforcing cords, which extend in a tire radial direction, in a tirecircumferential direction at a predetermined pitch and embedding thereinforcing cords in a rubber layer, are disposed extending between theleft and right side bead portions 3. Both ends of the carcass layer 4are made to sandwich a bead filler 6 around a bead core 5 that isembedded in the bead portions 3 and are folded back in a tire axialdirection from the inside to the outside. An innerliner layer 7 isdisposed inward of the carcass layer 4. Two belt layers 8, formed byarranging reinforcing cords, which extend inclined in the tirecircumferential direction, in the tire axial direction at apredetermined pitch and embedding these reinforcing cords in a rubberlayer, are disposed on an outer circumferential side of the carcasslayer 4 of the tread portion 1. The reinforcing cords of the two beltlayers 8 are inclined with respect to the tire circumferential directionand the direction of the reinforcing cords of the different layersintersect with each other. A belt cover layer 9 is disposed on the outercircumferential side of the belt layers 8. The tread portion 1 is formedfrom tread rubber layers 10 a and 10 b on the outer circumferential sideof the belt cover layer 9. The tread rubber layers 10 a and 10 b are captread and base tread, and preferably can be formed from the rubbercomposition of the present technology.

The rubber composition of the present technology contains a diene rubberand a reinforcing filler. The diene rubber contains at least one type ofstyrene-butadiene copolymer without exception. In the presentspecification, a polymer component formed from at least one type ofstyrene-butadiene copolymer is referred to as a “styrene-butadienecopolymer component”. In the present technology, the styrene-butadienecopolymer component satisfies characteristics (1) to (4) describedbelow. Note that, in the present specification, a moiety where a styreneunit in the main chain of the styrene-butadiene copolymer isozone-decomposed is referred to as “styrene-derived unit”, and a moietywhere a butadiene unit that has been polymerized by 1,2-bonding in themain chain is ozone-decomposed is referred to as “1,2-bondedbutadiene-derived unit”.

(1) A bonded styrene content is from 5 to 50 wt. %.

(2) When a decomposed component S1 having one styrene-derived unit and adecomposed component S1V1 having one styrene-derived unit and one1,2-bonded butadiene-derived unit are measured by subjecting adecomposed component obtained by ozone decomposition to gel permeationchromatography (GPC), a total of styrene contents of the decomposedcomponent S1 and the decomposed component S1V1 is less than 80 wt. % ofthe bonded styrene content, and a total of styrene content of thedecomposed component S1V1 is less than 10 wt. % of the bonded styrenecontent.

(3) When the decomposed component obtained by ozone decomposition ismeasured by liquid chromatography-mass spectrometer (LCMS), anintegrated intensity of a decomposed component S1V2 having onestyrene-derived unit and two 1,2-bonded butadiene-derived units is 15%or greater of an integrated intensity of all the decomposed componentscontaining a styrene-derived unit.

(4) A vinyl content of butadiene moiety is 50% or greater.

When the styrene-butadiene copolymer component is formed from astyrene-butadiene copolymer alone, the styrene-butadiene copolymer aloneneeds to satisfy all of the characteristics (1) to (4) described above.

Furthermore, when the styrene-butadiene copolymer component is formedfrom a blend of a plurality of styrene-butadiene copolymers, thestyrene-butadiene copolymer component as a whole needs to satisfy all ofthe characteristics (1) to (4) described above. As long as thestyrene-butadiene copolymer component as a whole satisfies all of thecharacteristics (1) to (4), each of the styrene-butadiene copolymersconstituting the blend may satisfy, or not satisfy, all of thecharacteristics (1) to (4) described above. Preferably, each of thestyrene-butadiene copolymer constituting the blend satisfies all of thecharacteristics (1) to (4). By allowing the styrene-butadiene copolymercomponent to be composed of two or more type of styrene-butadienecopolymers satisfying all the characteristics (1) to (4), even betterwear resistance and rubber strength of the rubber composition areachieved. Note that, in the present specification, the rubber strengthrefers to a tensile stress at 100% elongation in the tensile test inaccordance with JIS K6251.

In the present technology, the styrene-butadiene copolymer component has(1) a bonded styrene content of 5 to 50 wt. %, and preferably 10 to 40wt. %. By setting the styrene content of the styrene-butadiene copolymercomponent to be within such a range, excellent balance of wet skidcharacteristics and wear resistance and rubber strength of the rubbercomposition can be achieved. As a result, the rubber composition thatsolves problems of the present technology can be obtained. When thestyrene content of the styrene-butadiene copolymer component is lessthan 5 wt. %, the wet skid characteristics, and wear resistance andrubber strength are deteriorated. When the styrene content of thestyrene-butadiene copolymer component is greater than 50 wt. %, theglass transition temperature (Tg) of the styrene-butadiene copolymercomponent increases, thereby deteriorating the balance of viscoelasticcharacteristics and making it difficult to achieve the effect ofreducing heat build-up. That is, the balance of hysteresis loss and wetskid characteristics is deteriorated. Note that the styrene content ofthe styrene-butadiene copolymer component is measured by ¹H-NMR.

In the styrene-butadiene copolymer component used in the presenttechnology, (2) an ozone-decomposed component S1 having onestyrene-derived unit and an ozone-decomposed component S1V1 having onestyrene-derived unit and one 1,2-bonded butadiene-derived unit aremeasured by subjecting a decomposed component obtained by ozonedecomposition to gel permeation chromatography (GPC). At this time, thetotal of styrene contents of the ozone-decomposed component S1 and theozone-decomposed component S1V1 is less than 80 wt. % of the bondedstyrene content, and the total of a styrene content of theozone-decomposed component S1V1 is less than 10 wt. % of the bondedstyrene content.

The styrene-butadiene copolymer is a copolymer of styrene and butadiene,and is formed from styrene repeating units (styrene units) and butadienerepeating units (butadiene units). The butadiene unit is formed from amoiety where butadiene is polymerized at the 1,2-bond (ethylenerepeating unit having a vinyl group as a side chain thereof) and amoiety where butadiene is polymerized at the 1,4-bond (divalent grouprepeating unit of 2-butylene). Furthermore, a moiety that waspolymerized at the 1,4-bond is formed from repeating units oftrans-2-butylene structure and repeating units of cis-2-butylenestructure.

When a styrene-butadiene copolymer is subjected to ozone decomposition,the moiety polymerized at the 1,4-bond is cleaved. Furthermore, thevinyl group of the side chain is oxidized to be a hydroxymethyl group.As a result, in the styrene-butadiene copolymer, as an ozone-decomposedcomponent, a repeating unit which is sandwiched by adjacent twobutadiene units polymerized at the 1,4-bonds is produced. For example,when a moiety in which only one styrene unit in the main chain issandwiched by two butadiene units polymerized at the 1,4-bonds issubjected to ozone decomposition, a compound represented by the generalformula (I) below is produced. In the present specification, thecompound represented by the general formula (I) is referred to as“ozone-decomposed component S1”.

Furthermore, when a moiety in which one styrene unit and one butadieneunit that was polymerized at the 1,2-bond in the main chain weresandwiched by adjacent butadiene units polymerized at the 1,4-bonds issubjected to ozone decomposition, compounds represented by the generalformulas (II) and (III) are produced. In the present specification, thecompounds represented by the general formulas (II) and (III) arereferred to as “ozone-decomposed component S1V1”.

Furthermore, when a moiety in which one styrene unit and two butadieneunits polymerized at the 1,2-bond in the main chain were sandwiched byadjacent butadiene units polymerized at the 1,4-bonds is subjected toozone decomposition, compounds represented by the general formulas (IV)to (VI) below are produced. In the present specification, the compoundsrepresented by the general formulas (IV) to (VI) are referred to as“ozone-decomposed component S1V2”.

As described above, a moiety which is sandwiched by two adjacentbutadiene units polymerized at the 1,4-bonds produces a decomposedcomponent in which a styrene-derived unit and/or 1,2-bondedbutadiene-derived unit(s) is sandwiched by hydroxyethyl groups at theboth terminals by the ozone decomposition. Furthermore, 1,4-butanediolis produced from a moiety in which two or more butadiene unitspolymerized at the 1,4-bond are continuously repeated.

When the decomposed component obtained by ozone decomposition of thestyrene-butadiene copolymer component used in the present technology ismeasured by gel permeation chromatography (GPC), the total of thestyrene content of the ozone-decomposed component S1 and the styrenecontent of the ozone-decomposed component S1V1 is less than 80 wt. %,preferably less than 70 wt. %, more preferably from 20 to 65 wt. %, andeven more preferably from 40 to 60 wt. %, of the bonded styrene content.Note that “decomposed component having one styrene-derived unit” refersto the ozone-decomposed component S1 having one styrene-derived unit andthe ozone-decomposed component S1V1 having one styrene-derived unit andone 1,2-bonded butadiene-derived unit, as described above. By measuringthe ozone-decomposed component by gel permeation chromatography (GPC),the number of moles of the styrene-derived unit in each of thedecomposed component can be determined. The weight of the styrene ineach of the ozone-decomposed component is calculated based on the numberof moles of the styrene-derived unit. The total styrene content of theozone-decomposed components S1 and S1V1 determined as described aboveneeds to be less than 80 wt. % of the bonded styrene content. By this,even better wear resistance can be achieved.

Furthermore, in addition to the description above, when the decomposedcomponent obtained by ozone decomposition of the styrene-butadienecopolymer component used in the present technology is measured by gelpermeation chromatography (GPC), the total of the styrene content of thedecomposed component S1V1 having one styrene-derived unit and one1,2-bonded butadiene-derived unit is less than 10 wt. %, and preferablyfrom 3 wt. % or greater and less than 10 wt. %, of the bonded styrenecontent. The ozone-decomposed component S1V1 is an ozone-decomposedcomponent consisting of one styrene-derived unit and one 1,2-bondedbutadiene-derived unit as described above and corresponds to thedecomposed component represented by the general formulas (II) and (III)described above. By measuring the ozone-decomposed component by gelpermeation chromatography (GPC), the number of moles of the decomposedcomponent represented by the general formulas (II) and (III) isdetermined, and the weight of the styrene is calculated based on this.The styrene content of the ozone-decomposed component having onestyrene-derived unit and one 1,2-bonded butadiene-derived unit needs tobe less than 10 wt. % of the bonded styrene content. By this, excellentwear resistance and tensile stress can be achieved.

In the present specification, the method of subjecting thestyrene-butadiene copolymer component to ozone decomposition and themeasurement of the ozone decomposition are performed by methodsdescribed in Tanaka et al., [Polymer, 22, 1721(1981)] and[Macromolecules, 16, 1925(1983)]. Note that, in the analysis methoddescribed in Tanaka et al., the total of the general formulas (I), (II),and (III) is referred to as “styrene single chain”. On the other hand,the present technology focuses on the total amount of theozone-decomposed component S1 having one styrene-derived unit and theozone-decomposed component S1V1 having one styrene-derived unit and one1,2-bonded butadiene-derived unit (S1+S1V1; total of the decomposedcomponent represented by the general formulas (I), (II), and (III)described above) as well as the decomposed component having onestyrene-derived unit and one 1,2-bonded butadiene-derived unit (S1V1;decomposed component represented by the general formulas (II) and (III)described above) as described above, and these are analyzed separately.

In the present specification, the following conditions can be employedfor the measurement of the ozone-decomposed component by gel permeationchromatography (GPC).

Measurement instrument: LC-9104 (manufactured by Japan AnalyticalIndustry Co., Ltd.)

Column: Two columns of JAIGEL-1H and two columns of JAIGEL-2H areconnected in series for use (both are manufactured by Japan AnalyticalIndustry Co., Ltd.)

Detector: UV DETECTOR 3702 (manufactured by Japan Analytical IndustryCo., Ltd.)

Differential refractometer RI DETECTOR RI-7 (manufactured by JapanAnalytical Industry Co., Ltd.)

Eluent: Chloroform

Column temperature: Room temperature

In the styrene-butadiene copolymer component used in the presenttechnology, (3) when the decomposed component obtained by ozonedecomposition is measured by liquid chromatography-mass spectrometer(LCMS), an integrated intensity of a decomposed component S1V2 havingone styrene-derived unit and two 1,2-bonded butadiene-derived units is15% or greater, and preferably from 15 to 40%, of an integratedintensity of all the decomposed components containing a styrene-derivedunit. By setting the integrated intensity of the decomposed componentS1V2 to 15% or greater, even better wear resistance can be achieved.Furthermore, tensile stress can be also enhanced. Note that thedecomposed component S1V2 having one styrene-derived unit and two1,2-bonded butadiene-derived units is an ozone-decomposed componenthaving one styrene-derived unit and two 1,2-bonded butadiene-derivedunit as described above and corresponds to the decomposed componentrepresented by the general formulas (IV), (V), and (VI) described above.By measuring these by a liquid chromatography-mass spectrometer (LCMS),an integrated intensity of a peak that is intrinsic to each decomposedcomponent having the molecular weight of the general formulas (IV), (V),and (VI) is determined.

The integrated intensity of each of the decomposed component can bedetermined by using the measurement method and analysis method describedbelow. Since molecules of each decomposed component can be detected in astate of sodium-added ions, each mass chromatogram is extracted based onthe mass spectrum. The mass spectrum of the sodium-added ion is 333.21in the case of the decomposed component S1V2 having one styrene-derivedunit and two 1,2-bonded butadiene-derived units. In the masschromatogram of 333.21, the peak of the decomposed component S1V2 isdetermined, and an integrated intensity A [S1V2] thereof is determined.Similarly, the integrated intensity of all the decomposed componentsincluding the other styrene-derived unit is determined, and the sum A[total] thereof is determined. The proportion of the integratedintensity A [S1V2] of the ozone-decomposed component S1V2 having onestyrene-derived unit and two 1,2-bonded butadiene-derived units relativeto the sum A [total] of the integrated intensity of all the decomposedcomponents including styrene-derived unit is calculated by a calculationformula: A [S1V2]/A [total]×100.

In the present specification, the following conditions can be employedfor the measurement of the ozone-decomposed component by liquidchromatography-mass spectrometer (LCMS).

Liquid chromatograph: Alliance 2695 (manufactured by Nihon Waters K.K.)

Mass analyzer: ZQ2000 (manufactured by Nihon Waters K.K.)

Column: Hydrosphere C18 (manufactured by YMC Co., Ltd.; inner diameter:2.0 mm; length: 150 mm; particle size: 3 μm)

Injection amount: 5 (approximately 10 mg/mL)

Mobile phase A: Water

Mobile phase B: Methanol

Flow rate: 0.2 mL/min

Time program: B conc. 20% (0 minutes)→100% (35 minutes)→100% (50minutes)

Ion source temperature: 120° C.

Desolvation temperature: 350° C.

Cone voltage: 40 V

Ionization method: (ESI positive mode)

Mass analysis condition: Scan measurement, mass range m/z 50-2000

In the styrene-butadiene copolymer component used in the presenttechnology, (4) the vinyl content of the butadiene moiety is 50% orgreater, and preferably from 50 to 65%. By setting the vinyl content ofthe butadiene moiety in the styrene-butadiene copolymer component to be50% or greater, it is possible to maintain and enhance wear resistanceof the rubber composition and to achieve the balance between hysteresisloss and wet skid characteristics. That is, by setting the vinyl contentof the butadiene moiety to be 50% or greater, rubber strength and wearresistance can be enhanced and increase in hysteresis loss can besuppressed. Note that the vinyl content of the butadiene moiety ismeasured by ¹H-NMR.

The content of the styrene-butadiene copolymer component having thecharacteristics (1) to (4) is preferably 40 wt. % or greater, morepreferably from 60 to 100 wt. %, and even more preferably from 80 to 100wt. %, per 100 wt. % of the diene rubber. By allowing 40 wt. % orgreater of the styrene-butadiene copolymer component specified by thecharacteristics (1) to (4) to be contained, excellent wear resistanceand rubber strength of the rubber composition are achieved.

The rubber composition of the present technology may contain anotherdiene rubber except the styrene-butadiene copolymer component satisfyingall the characteristics (1) to (4). Examples of such another dienerubber include natural rubber (NR), polyisoprene rubber (IR),polybutadiene rubber (low cis-BR), high-cis BR, high-trans BR (from 70to 95% of the trans-bond content in the butadiene moiety),styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber,solution polymerized random styrene-butadiene-isoprene copolymer rubber,emulsion polymerized random styrene-butadiene-isoprene copolymer rubber,emulsion polymerized styrene-acrylonitrile-butadiene copolymer rubber,acrylonitrile-butadiene copolymer rubber, high vinyl SBR-low vinyl SBRblock copolymer rubber, polyisoprene-SBR block copolymer rubber, andpolystyrene-polybutadiene-polystyrene block copolymer.

The content of such another diene rubber is preferably 60 wt. % or less,more preferably from 0 to 40 wt. %, and even more preferably from 0 to20 wt. %, per 100 wt. % of the diene rubber. By allowing another dienerubber to be contained, various physical properties such as wearresistance and rubber strength can be enhanced.

The rubber composition of the present technology contains a diene rubberand a reinforcing filler. Examples of the reinforcing filler includeinorganic fillers, such as carbon black, silica, clay, aluminumhydroxide, calcium carbonate, mica, talc, aluminum oxide, titaniumoxide, and barium sulfate, and organic fillers such as, cellulose,lecithin, lignin, and dendrimer. Among these, at least one type selectedfrom the group consisting of a carbon black and a silica is preferablyblended.

By allowing the rubber composition to contain a carbon black, excellentwear resistance and rubber strength of the rubber composition can beachieved. The compounded amount of the carbon black is not particularlylimited but is preferably from 10 to 100 parts by weight, and morepreferably from 25 to 80 parts by weight, per 100 parts by weight of thediene rubber.

As the carbon black, carbon blacks such as furnace black, acetyleneblack, thermal black, channel black, and graphite may be blended. Amongthese, furnace black is preferred, and specific examples thereof includeSAF, ISAF, ISAF-HS, ISAF-LS, IISAF-HS, HAF, HAF-HS, HAF-LS, and FEF. Thecarbon black may be used alone or a combination of two or more types ofthese carbon blacks may be used. Furthermore, surface-treated carbonblacks obtained by subjecting these carbon blacks to chemicalmodification with various acid compounds or the like may be also used.

By allowing the rubber composition to contain a silica, excellent lowheat build-up and wet grip performance of the rubber composition can beachieved. The compounded amount of the silica is not particularlylimited but is preferably from 10 to 150 parts by weight, and morepreferably from 40 to 100 parts by weight, per 100 parts by weight ofthe diene rubber.

The silica may be any silica that is regularly used in rubbercompositions for tire treads. Examples thereof include wet methodsilica, dry method silica, carbon-silica in which silica is supported ona surface of carbon black (dual phase filler), surface-treated silicawhich is surface-treated with a silane coupling agent or a compoundhaving reactivity or miscibility in both the silica and rubber, such aspolysiloxane. Among these, wet method silica containing hydrous silicicacid as a main component is preferred.

In the present technology, the compounded amount of the reinforcingfiller including the silica and/or the carbon black is preferably from10 to 150 parts by weight, and more preferably from 40 to 100 parts byweight, per 100 parts by weight of the diene rubber. When the compoundedamount of the reinforcing filler is less than 10 parts by weight,reinforcing performance cannot be sufficiently obtained, and rubberhardness and tensile strength at break become insufficient. When thecompounded amount of the reinforcing filler is greater than 150 parts byweight, heat build-up is increased and tensile elongation at break isdecreased. Furthermore, wear resistance and processability aredeteriorated.

Blending of a silane coupling agent together with silica is preferred inthe rubber composition of the present technology since low heat build-upand wear resistance are further enhanced. By blending a silane couplingagent together with silica, dispersibility of silica is enhanced,thereby further increasing reinforcement action with the diene rubber.The compounded amount of the silane coupling agent is preferably from 2to 20 wt. %, and more preferably from 5 to 15 wt. %, relative to thecompounded amount of silica. When the compounded amount of the silanecoupling agent is less than 2 wt. % of the weight of the silica, theeffect of enhancing dispersibility of the silica cannot be sufficientlyobtained. Furthermore, when the compounded amount of the silane couplingagent is greater than 20 wt. %, the diene rubber component tends to beeasily gelled, thereby making it impossible to achieve predeterminedeffects.

The silane coupling agent is not particularly limited but is preferablya sulfur-containing silane coupling agent.

Examples thereof include bis-(3-triethoxysilylpropyl)tetrasulfide,bis(3-triethoxysilylpropyl)trisulfide,bis(3-triethoxysilylpropyl)disulfide,bis(2-(triethoxysilylethyl)tetrasulfide,bis(3-trimethoxysilylpropyl)tetrasulfide,bis(2-trimethoxysilylethyl)tetrasulfide,3-mercaptopropyltrimethoxysilane, 3-mercaptopropyldimethoxymethylsilane,3-mercaptopropyldimethylmethoxysilane, 2-mercaptoethyltriethoxysilane,3-mercaptopropyltriethoxysilane, mercaptosilane compounds such as thoseexemplified in JP-A-2006-249069 including VP Si363 manufactured byEvonik, 3-trimethoxysilylpropylbenzothiazoletetrasulfide,3-triethoxysilylpropylbenzothiazolyltetrasulfide,3-triethoxysilylpropylmethacrylatemonosulfide,3-trimethoxysilylpropylmethacrylatemonosulfide,3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide,3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide,2-triethoxysilylethyl-N,N-dimethylthiocarbamoyltetrasulfide,bis(3-diethoxymethylsilylpropyl)tetrasulfide,dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide,dimethoxymethylsilylpropylbenzothiazolyltetrasulfide,3-octanoylthiopropyltriethoxysilane,3-propionylthiopropyltrimethoxysilane, vinyltrimethoxysilane,vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane,3-glycidoxypropyltrimethoxysilane,3-glycidoxypropylmethyldimethoxysilane,β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,3-aminopropyltrimethoxysilane,N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane,N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, and the like.Furthermore, the silane coupling agent is an organosilicon compound, andexamples of the organosilicon compound include polysiloxane, siliconeoils in which at least one of organic groups, including an amino group,an epoxy group, a carbinol group, a mercapto group, a carboxyl group, ahydrogen group, a polyether group, a phenol group, a silanol group, anacryl group, a methacryl group, or a long-chain alkyl group, isintroduced to a side chain, both terminals, one terminal, or both ofside chain and both terminals of the polysiloxane, and siliconeoligomers obtained by subjecting at least one type of organosilane tocondensation reaction. Among these,bis-(3-triethoxysilylpropyl)tetrasulfide andbis(3-triethoxysilylpropyl)disulfide are preferred.

In addition to the components described above, various compoundingagents that are commonly used in rubber compositions for tire treads,such as vulcanization or cross-linking agents, vulcanizationaccelerators, anti-aging agents, processing aids, plasticizers, liquidpolymers, thermosetting resins, and thermoplastic resins may be blendedin the rubber composition of the present technology in accordance withconventional methods. These compounding agents can be kneaded by acommon method to obtain a rubber composition that can then be used forvulcanization or cross-linking. These compounding agents can becompounded in typical amounts conventionally used so long as the presenttechnology is not hindered. The rubber composition for tire treads canbe prepared by mixing the components described above using a publiclyknown rubber kneading machine such as a Banbury mixer, a kneader, and aroller.

Although the vulcanization or cross-linking agent is not particularlylimited; examples thereof include sulfurs, such as powder sulfur,precipitated sulfur, colloidal sulfur, insoluble sulfur, and highlydispersible sulfur; halogenated sulfurs, such as sulfur monochloride andsulfur dichloride; and organic peroxides, such as dicumyl peroxide anddi-tert-butyl peroxide. Among these, sulfur is preferred, and powdersulfur is particularly preferred. The vulcanization or cross-linkingagent may be used alone or a combination of two or more types of thesevulcanization and/or cross-linking agents may be used. The compoundedproportion of the vulcanizing agent is typically from 0.1 to 15 parts byweight, preferably from 0.3 to 10 parts by weight, and even morepreferably from 0.5 to 5 parts by weight, per 100 parts by weight of thediene rubber.

The vulcanization accelerator is not particularly limited, and examplesthereof include sulfenamide-based vulcanization accelerators, such asN-cyclohexyl-2-benzothiazylsulfenamide,Nt-butyl-2-benzothiazolesulfenamide,N-oxyethylene-2-benzothiazolesulfenamide,N,N′-diisopropyl-2-benzothiazolesulfenamide; guanidine-basedvulcanization accelerators, such as diphenylguanidine,di-o-tolylguanidine, and (o-tolyl)biguanidine; thiourea-basedvulcanization accelerators, such as diethyl thiourea; thiazole-basedvulcanization accelerators, such as 2-mercaptobenzothiazole,dibenzothiazyl disulfide, and zinc 2-mercaptobenzothiazole salt;thiuram-based vulcanization accelerators, such as tetramethylthiurammonosulfide and tetramethylthiuram disulfide; dithiocarbamic acid-basedvulcanization accelerators, such as sodium dimethyldithiocarbamate andzinc diethyldithiocarbamate; and xanthogenic acid-based vulcanizationaccelerators, such as sodium isopropylxanthogenate, zincisopropylxanthogenate, and zinc butylxanthogenate. Among these, avulcanization accelerator containing a sulfenamide-based vulcanizationaccelerator is particularly preferred. The vulcanization accelerator maybe used alone or a combination of two or more types of thesevulcanization accelerators may be used. The compounded amount of thevulcanization accelerator is preferably from 0.1 to 15 parts by weight,and more preferably from 0.5 to 5 parts by weight, per 100 parts byweight of the diene rubber.

The anti-aging agent is not particularly limited, and examples thereofinclude amine-based anti-aging agents, such as2,2,4-trimethyl-1,2-dihydroquinoline polymers,p,p′-dioctyldiphenylamine, N,N′-diphenyl-p-phenylenediamine, andN-phenyl-N′-1,3-dimethylbutyl-p-phenylenediamine; and phenol-basedanti-aging agents, such as 2,6-di-t-butyl-4-methylphenol and2,2′-methylenebis(4-methyl-6-t-butylphenol). The anti-aging agent may beused alone or a combination of two or more types of these anti-agingagents may be used. The compounded amount of the anti-aging agent ispreferably from 0.1 to 15 parts by weight, and more preferably from 0.5to 5 parts by weight, per 100 parts by weight of the diene rubber.

The processing aid is not particularly limited, and for example, higherfatty acids such as stearic acid, higher fatty amides such asstearamide, higher fatty amines such as stearylamine, higher aliphaticalcohols such as stearyl alcohol, partial esters of fatty acid andpolyhydric alcohol, such as glycerine fatty acid esters, fatty acidmetal salts such as zinc stearate, zinc oxide can be used. Although thecompounded amount is appropriately selected, the compounded amount ofthe higher fatty acid, higher fatty amide, higher alcohol, and/or fattyacid metal salt is preferably from 0.05 to 15 parts by weight, and morepreferably from 0.5 to 5 parts by weight, per 100 parts by weight of thediene rubber. The compounded amount of the zinc oxide is preferably from0.05 to 10 parts by weight, and more preferably from 0.5 to 3 parts byweight, per 100 parts by weight of the diene rubber.

The plasticizer used as a compounding agent is not particularly limited,and for example, aromatic, naphthene-based, paraffin-based,silicone-based, or similar extender oil is selected depending on theapplication. The used amount of the plasticizer is typically from 1 to150 parts by weight, preferably from 2 to 100 parts by weight, and evenmore preferably from 3 to 60 parts by weight, per 100 parts by weight ofthe diene rubber. When the used amount of the plasticizer is within thisrange, dispersing effect of the reinforcing agent, tensile strength,wear resistance, heat resistance, and the like are well-balanced at ahigh level. Examples of other plasticizers include diethylene glycol,polyethylene glycol, and silicone oils.

The thermosetting resin is not particularly limited, and examplesthereof include resorcin-formaldehyde resins, phenol-formaldehyderesins, urea-formaldehyde resins, melamine-formaldehyde resins, andphenol derivative-formaldehyde resins. Specific examples thereof includethermosetting resins that are cured or polymerized by heating or byapplying heat and a methylene donor, such as m-3,5-xylenol-formaldehyderesins and 5-methylresorcin-formaldehyde resins; other guanamine resins,diallylphthalate resins, vinyl ester resins, phenolic resins,unsaturated polyester resins, furan resins, polyimide resins,polyurethane resins, melamine resins, and urea resins, epoxy resins.

The thermosetting resin is not particularly limited, and examples ofgeneral purpose thermoplastic resins include polystyrene-based resins,polyethylene-based resins, polypropylene-based resins, polyester-basedresins, polyamide-based resins, polycarbonate-based resins,polyurethane-based resins, polysulfone-based resins, polyphenyleneether-based resins, polyphenylene sulfide-based resins. In addition,examples thereof include aromatic hydrocarbon-based resins, such asstyrene-α-methylstyrene resins, indene-isopropenyltoluene resins, andcoumarone-indene resins, hydrocarbon resins, such as dicyclopentadieneresins and petroleum resins including 1,3-pentadiene, pentene,methylbutene, or the like as the main ingredient, alkylphenol resins,modified phenolic resins, terpene phenol resins, terpene-based resins,and aromatic modified terpene resins.

Since the rubber composition of the present technology is to enhancerubber strength and wear resistance to or beyond conventional levels,steering stability and wear resistance of a pneumatic tire can beenhanced to or beyond conventional levels.

The rubber composition of the present technology can be suitably used incap tread portions, undertread portions, sidewall portions, bead fillerportions, coating rubbers for cord such as carcass layers, belt layers,and belt cover layers, side reinforcing rubber layers having a crescentshaped cross section used in run flat tires, and rim cushion portions ofpneumatic tires. A pneumatic tire manufactured using the rubbercomposition of the present technology in these members can maintainand/or enhance steering stability, wear resistance, and durability to orbeyond conventional levels due to the enhanced rubber strength and wearresistance.

The present technology is further described below by Examples. However,the scope of the present technology is not limited to these Examples.

EXAMPLES

A styrene-butadiene copolymer component in which 9 types of styrenebutadiene copolymers are each used alone or blended in a compoundingratio shown in Table 1 or 2 is prepared and used to measure (1) thebonded styrene content; (2) the total proportion of the styrene contentsof the ozone-decomposed component S1 having one styrene-derived unit andthe ozone-decomposed component S1V1 having one styrene-derived unit andone 1,2-bonded butadiene-derived unit (S1+S1V1; wt. %) relative to thebonded styrene content, and the total proportion of the styrene contentof the ozone-decomposed component S1V1 having one styrene-derived unitand one 1,2-bonded butadiene-derived unit (S1V1; wt. %) relative to thebonded styrene content; (3) the proportion of the integrated intensityof the decomposed component S1V2 having one styrene-derived unit and two1,2-bonded butadiene-derived units relative to the integrated intensityof all the decomposed products having a styrene-derived unit (S1V2; %);and (4) the vinyl content of butadiene moiety. Furthermore, since NS460,Nipol 1739, E581, and NS570 are oil extended products, net compoundedamounts of the rubber components are shown in parentheses in addition tothe actual compounded amounts.

(1) The bonded styrene content and (4) the vinyl content of thebutadiene moiety of the styrene-butadiene copolymer component weremeasured by ¹H-NMR.

The ozone decomposition conditions of the styrene-butadiene copolymercomponent were as described above. Furthermore, (2) the total proportionof the styrene contents of the ozone-decomposed component S1 having onestyrene-derived unit and the ozone-decomposed component S1V1 having onestyrene-derived unit and one 1,2-bonded butadiene-derived unit (S1+S1V1;wt. %) relative to the bonded styrene content, and the total proportionof the styrene content of the ozone-decomposed component S1V1 having onestyrene-derived unit and one 1,2-bonded butadiene-derived unit (S1V1;wt. %) relative to the bonded styrene content were measured by gelpermeation chromatography (GPC). The measurement conditions of the gelpermeation chromatography (GPC) were as described above.

Furthermore, (3) the proportion of the integrated intensity of thedecomposed component S1V2 having one styrene-derived unit and two1,2-bonded butadiene-derived units relative to the integrated intensityof all the decomposed components including styrene-derived unit (S1V2;%) were measured by liquid chromatography-mass spectrometer (LCMS). Themeasurement conditions of the liquid chromatography-mass spectrometer(LCMS) were as described above.

Fourteen types of the rubber compositions formed from thestyrene-butadiene copolymer components shown in Tables 1 and 2 (singlestyrene-butadiene copolymer or a blend of a plurality ofstyrene-butadiene copolymers) and other diene rubbers (Examples 1 to 10and Comparative Examples 1 to 4) using the compounding agents shown inTable 3 as common formulation, except the sulfur and the vulcanizationaccelerator, were mixed in a 1.7 L sealed Banbury mixer for 6 minutes,discharged from the mixer at 150° C., and cooled at room temperature.Next, the mixture was mixed again for 3 minutes using the 1.7 L sealedBanbury mixer and discharged. Then, the sulfur and the vulcanizationaccelerators were mixed using an open roll to prepare a rubbercomposition. The obtained rubber composition was vulcanized in apredetermined mold at 160° C. for 30 minutes to produce a vulcanizedrubber test piece. Using the obtained vulcanized rubber test piece,tensile characteristics (100% tensile stress) and wear resistance wereevaluated by the following measurement methods.

Tensile Stress Characteristics (100% Tensile Stress)

Using the obtained vulcanized rubber test piece, a JIS No. 3dumbbell-shaped test piece was produced in accordance with JIS K 6251and subjected to a tensile test at a tensile test speed of 500 mm/min atroom temperature (20° C.) to measure 100% tensile stress at 100%elongation. The obtained results are shown as index values in the “100%Tensile stress” rows of Tables 1 and 2, with the value of ComparativeExample 1 expressed as an index of 100. A larger index value of 100%tensile stress indicates higher 100% tensile stress and superiorsteering stability when a tire is formed.

Wear Resistance

The amount of wear of the obtained vulcanized rubber test piece wasmeasured in accordance with JIS K6264, using a Lambourn abrasion testmachine (manufactured by Iwamoto Seisakusho Co., Ltd.) under thefollowing conditions: a load of 15.0 kg (147.1 N) and slip ratio of 25%.From the obtained results, reciprocal values were calculated, and thecalculated values are shown as index values in the “Wear resistance”rows of Tables 1 and 2, with the reciprocal of the amount of wear ofComparative Example 1 expressed as an index of 100. A larger index valueof the wear resistance indicates superior wear resistance.

TABLE 1 Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 NS116 Part by weight 100 30 30 NS460 Partby weight  49.5 (36) 5260H Part by weight 5270H Part by weight 5220MPart by weight Nipol 1739 Part by weight 96.25 (70) E581 Part by weight74.25 (54) NS570 Part by weight 96.25 (70) BR Part by weight 10 Oil Partby weight 37.5 11.25 3.75 11.25 Bonded styrene content wt. % 20.9 34.731.8 34.1 Vinyl content % 63.8 41.5 50.6 32.0 S1 + S1V1 wt. % 65.2 67.239.3 51.1 S1V1 wt. % 24.7 13.2 10.5 8.8 S1V2 (integrated intensityratio) % 27.8 28.4 20.5 17.1 Wear resistance Index value 100 94 98 91100% Tensile stress Index value 100 109 106 113 Example 1 Example 2Example 3 Example 4 NS116 Part by weight NS460 Part by weight 5260H Partby weight 70 5270H Part by weight 30 70 100 80 5220M Part by weight 30Nipol 1739 Part by weight E581 Part by weight 27.5 (20) NS570 Part byweight BR Part by weight Oil Part by weight 37.5 37.5 37.5 30 Bondedstyrene content wt. % 25.7 22.3 20.6 24.4 Vinyl content % 57.6 52.5 63.654.6 S1 + S1V1 wt. % 43.1 50.9 48.7 48.0 S1V1 wt. % 6.1 7.7 4.3 3.9 S1V2(integrated intensity ratio) % 15.9 33.9406207 33.0 28.9 Wear resistanceIndex value 106 107 108 104 100% Tensile stress Index value 102 100 100105

TABLE 2 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10Y031 Part by weight 70 80 5270H Part by weight 70 70 95 80 E581 Part byweight 41.25 (30) NS570 Part by weight 27.5 (20) 27.5 (20) Naturalrubber Part by weight 30 BR Part by weight 30 5 Oil Part by weight 37.537.5 37.5 30 26.25 30 Bonded styrene content wt. % 20.6 20.6 20.6 24.629.8 29.8 Vinyl content % 63.6 63.6 63.6 57.3 53.0 52.4 S1 + S1V1 wt. %48.7 48.7 48.7 52.6 49.3 58.4 S1V1 wt. % 4.3 4.3 4.3 5.1 6.6 6.1 S1V2(integrated intensity ratio) % 33.0 33.0 33.0 32.1 15.4 15.7 Wearresistance Index value 108 108 108 104 102 102 100% Tensile stress Indexvalue 100 100 100 104 108 109

The types of raw materials used in Tables 1 and 2 are shown below.

NS116: NS116, manufactured by Zeon Corporation; bonded styrene content:20.9 wt. %; vinyl content: 63.8%; non-oil extended product

NS460: NS460, manufactured by Zeon Corporation; bonded styrene content:25.1 wt. %; vinyl content: 62.8%; oil extended product in which 37.5parts by weight of oil component was added to 100 parts by weight of SBR

Y031: Asaprene Y031, manufactured by Asahi Kasei Chemicals Corporation;bonded styrene content: 27.1 wt. %; vinyl content: 57.5%; non-oilextended product

5260H: 5260H, manufactured by Korea Kumho Petrochemica; bonded styrenecontent: 27.9 wt. %; vinyl content: 55.0%; non-oil extended product

5270H: 5270H, manufactured by Korea Kumho Petrochemica; bonded styrenecontent: 20.6 wt. %; vinyl content: 63.6%; non-oil extended product

5220M: 5220M, manufactured by Korea Kumho Petrochemica; bonded styrenecontent: 26.3 wt. %; vinyl content: 26.5%; non-oil extended product

Nipol 1739: Nipol 1739, manufactured by Zeon Corporation; bonded styrenecontent: 39.8 wt. %; vinyl content: 18.4%; oil extended product in which37.5 parts by weight of oil component was added to 100 parts by weightof SBR

E581: E581, manufactured by Asahi Kasei Chemicals Corporation; bondedstyrene content: 35.6 wt. %; vinyl content: 41.3%; oil extended productin which 37.5 parts by weight of oil component was added to 100 parts byweight of SBR

NS570: NS570, manufactured by Zeon Corporation; bonded styrene content:40.6 wt. %; vinyl content: 19.0%; oil extended product in which 37.5parts by weight of oil component was added to 100 parts by weight of SBR

NR: Natural rubber, TSR20

BR: Polybutadiene; Nipol BR1220, manufactured by Zeon Corporation

Oil: Extract No. 4S, manufactured by Showa Shell Sekiyu K.K.

TABLE 3 Common formulation of rubber composition Silica 70 part byweight Silane coupling agent 5.6 part by weight Carbon black 5 part byweight Zinc oxide 3 part by weight Stearic acid 2 part by weightAnti-aging agent 1.5 part by weight Wax 1 part by weight Sulfur 1.5 partby weight Vulcanization accelerator-1 1.7 part by weight Vulcanizationaccelerator-2 2 part by weight

The types of raw materials used as per Table 3 are described below.

Silica: Nipsil AQ, manufactured by Nippon Silica Co., Ltd.

Silane coupling agent: Sulfide-based silane coupling agent; Si69VP,manufactured by Degussa

Carbon black: Shoblack N339M, manufactured by Showa Cabot K.K.

Zinc oxide: Zinc Oxide #3, manufactured by Seido Chemical Industry Co.,Ltd.

Stearic acid: Stearic acid, manufactured by NOF Corporation

Anti-aging agent: Santoflex 6PPD, manufactured by Solutia Europe

Wax: Paraffin wax, manufactured by Ouchi Shinko Chemical Industrial Co.,Ltd.

Sulfur: Oil-treated sulfur, manufactured by Karuizawa Refinery Ltd.

Vulcanization accelerator-1: Sanceller CM-PO (CZ), manufactured bySanshin Chemical Industry Co., Ltd.

Vulcanization accelerator-2: Sanceller D-G (DPG), manufactured bySanshin Chemical Industry Co., Ltd.

As is clear from Tables 1 and 2, it was confirmed that the rubbercompositions of Examples 1 to 10 enhanced the wear resistance and the100% tensile stress.

The rubber composition of Comparative Example 2 deteriorated in the wearresistance since the vinyl content of the butadiene moiety of thestyrene-butadiene copolymer component was less than 50%, and theproportion (S1V1) of the total styrene content of the ozone-decomposedproduct having one styrene-derived unit and one 1,2-bondedbutadiene-derived unit relative to the bonded styrene content was 10 wt.% or greater.

The rubber composition of Comparative Example 3 deteriorated in the wearresistance since, in the styrene-butadiene copolymer component, theproportion (S1V1) of the total styrene content of the ozone-decomposedproduct having one styrene-derived unit and one 1,2-bondedbutadiene-derived unit relative to the bonded styrene content was 10 wt.% or greater.

The rubber composition of Comparative Example 4 deteriorated in the wearresistance since the vinyl content of the butadiene moiety of thestyrene-butadiene copolymer component was less than 50%.

1. A rubber composition comprising: a diene rubber containing at leastone type of styrene-butadiene copolymer; and a reinforcing filler, astyrene-butadiene copolymer component formed from the at least one typeof styrene-butadiene copolymer having characteristics (1) to (4): (1) abonded styrene content being from 5 to 50 wt. %; (2) when a decomposedcomponent S1 having one styrene-derived unit and a decomposed componentS1V1 having one styrene-derived unit and one 1,2-bondedbutadiene-derived unit are measured by subjecting a decomposed componentobtained by ozone decomposition to gel permeation chromatography (GPC),a total of styrene contents of the decomposed component S1 and thedecomposed component S1V1 being less than 80 wt. % of the bonded styrenecontent, and a total of styrene content of the decomposed component S1V1being less than 10 wt. % of the bonded styrene content; (3) when thedecomposed component obtained by ozone decomposition is measured byliquid chromatography-mass spectrometer (LCMS), an integrated intensityof a decomposed component S1V2 having one styrene-derived unit and two1,2-bonded butadiene-derived units being 15% or greater of an integratedintensity of all the decomposed components containing a styrene-derivedunit; and (4) a vinyl content of butadiene moiety being 50% or greater.2. The rubber composition according to claim 1, wherein the diene rubberfurther comprises at least one type selected from the group consistingof natural rubber, polyisoprene, and polybutadiene.
 3. The rubbercomposition according to claim 1, wherein the reinforcing filler isformed from at least one type selected from the group consisting of asilica and a carbon black.
 4. A pneumatic tire comprising the rubbercomposition described in claim
 1. 5. The pneumatic tire according toclaim 4, wherein the rubber composition is used in a cap tread.
 6. Therubber composition according to claim 2, wherein the reinforcing filleris formed from at least one type selected from the group consisting of asilica and a carbon black.
 7. A pneumatic tire comprising the rubbercomposition described in claim 6, wherein the rubber composition is usedin a cap tread.